In the past few decades, the petroleum industry has invested heavily in the development of marine seismic survey techniques that yield knowledge of subterranean formations beneath a body of water in order to find and extract valuable mineral resources, such as oil and natural gas. High-resolution seismic images of a subterranean formation are essential for quantitative seismic interpretation and improved reservoir monitoring. For a typical marine seismic survey, an exploration-seismology vessel tows one or more seismic sources and one or more streamers below the surface of the water and over a subterranean formation to be surveyed for mineral deposits. The vessel contains seismic acquisition equipment, such as navigation control, seismic source control, seismic receiver control, and recording equipment. The seismic source control causes the one or more seismic sources, which are typically air guns, to produce acoustic impulses at selected times. Each impulse is a sound wave that travels down through the water and into the subterranean formation. At each interface between different types of rock, a portion of the sound wave is refracted, a portion of the sound wave is transmitted, and another portion is reflected back into the body of water to propagate toward the surface. The streamers towed behind the vessel are elongated cable-like structures. Each streamer includes a number of seismic receivers or sensors that detect pressure and/or particle motion changes in the water created by the sound waves reflected back into the water from the subterranean formation.
The sounds waves that propagate upwardly from the subterranean formation are referred to as “up-going” wavefields that are detected by the receivers and converted into seismic signals that are recorded by the recording equipment and processed to produce seismic images that characterize the geological structure and properties of the subterranean formation being surveyed. However, the up-going sound waves continue to propagate beyond the streamers to the water surface from which the waves are downwardly reflected or “down-going” wavefields that are also detected by the receivers. The down-going waves are referred to as “ghost reflections.” The ghost reflections can be phase-shifted by as much as 180 degrees relative to the up-going waves. The ghost reflections amplify some frequencies and attenuate other frequencies in the waves detected by the receivers and are sent as “ghost” signals from the receivers to the recording equipment. The ghost signals are manifest as spectral notches in the recorded seismic signals, which make it difficult to obtain accurate high-resolution seismic images of the subterranean formation. As a result, those working in the petroleum industry continue to seek systems and methods to remove the effects of ghost reflections, or “deghost,” seismic signals.